Enterprise Architecture (EA) projects require analyzing and designing across the whole enterprise and its environment. Enterprise architects, therefore, frequently develop enterprise models that span from the markets in which the organization operates down to the implementation of the IT systems that support its operations. In this paper, we present SEAM for EA: a method for defining an enterprise model in which all the systems are systematically represented with the same modeling ontology. We base our modeling ontology on the foundation modeling concepts defined in Part 2 of ISO/ITU Standard “Reference Model of Open Distributed Processing” (RM-ODP). This work has two contributions to Enterprise Architecture: The SEAM for EA method itself and the use of part 2 of the RM-ODP standard as a modeling ontology.